Brake power booster with diaphragm position sensing devices

Abstract

In an anti-lock brake control system having a vacuum brake power booster and a tandem master cylinder, in which the brake pedal is controlled to be positioned forwardly of the initial return position during the anti-lock control mode. This is achieved by variation of the rate of delivery of an auxiliary pump as by switching the pump motor on and off by a switch actuated by the diaphragm of the power booster to provide a signal of the pedal position at the start of an anti-lock control phase. Various switching arrangements described include a Bowden-cable pulled by the diaphragm, a mechanical or an optical switch actuated by the rolling lip of the diaphragm, or an approach switch detecting the approach of the diaphragm and cam-assembly. The core (53) of the Bowden cable (54) is connected with the diaphragm plate (52) of the vacuum brake power booster. The core (53) moves the trigger cam (64). The switch (18) is actuated by the movement of the trigger cam (64).

What is claimed is: 
     
       1. A braking pressure control system having a slip control mode for a hydraulic brake system for automotive vehicles having a brake pedal, a master cylinder having at least one working piston and a working chamber supplied with fluid able to be pressurized by stroking of said working piston, means operatively coupling said brake pedal and said working piston to allow stroking by advance of said brake pedal from an initial return position to an advanced end position, wheel cylinders, said working chamber in communication with said wheel cylinders to generate a fluid pressure therein, said system further having at least one pump having an output flow directed to an outlet in communication with said working chamber for supplying hydraulic fluid to controllably position said at least one working piston of said master cylinder, said pump including means for varying said output flow therefrom, a pressure modulator modulating said fluid pressure in said wheel cylinders during said slip control mode, said pressure modulator including an opening valve and a shut off valve for each wheel cylinder, said system also including wheel sensors for generating signals indicating wheel slip and an electronic control unit processing said wheel sensor signals to form corrective signals for operating said opening valves and shut-off valves of the pressure modulator, said system further including a brake power booster composed of a booster housing and a diaphragm in said booster housing mounted to be able to be advanced to various positions therein, and means for controllably creating a pressure difference across said diaphragm to generate a booster force, means for coupling said diaphragm to said working piston to assist brake pedal stroking thereof by said generated force, switch means responsive to said position of said diaphragm to actuate said pump at a varying output level in correspondence with said position of said diaphragm corresponding to said position of said working piston from said initial return position to said advanced end position. 
     
     
       2. A braking pressure control system as claimed in claim 1, wherein said diaphragm has a rolling lip and wherein said switch means includes a switch operated by engagement with said rolling lip after advance of said diaphragm in said booster housing a predetermined distance in the direction of brake application. 
     
     
       3. A braking pressure control system as claimed in claim 2, wherein said switch means includes a mechanical limit switch mounted in said booster housing, said mechanical limit switch including a roller type lever actuatable by said rolling lip of said diaphragm. 
     
     
       4. A braking pressure control system as claimed in claim 2, wherein said switch includes a magnetic limit switch incorporating a reed contact, actuatable by said rolling lip of said diaphragm, said rolling lip carrying a magnetized section. 
     
     
       5. A barking pressure control system as claimed in claim 2, wherein said switch includes a photo-electric switch mounted in said booster housing, a portion of said rolling lip forming a light barrier, after a predetermined advance of said diaphragm in the direction of brake application. 
     
     
       6. A brake pressure control system as claimed in claim 5, wherein a reflective portion is formed on said rolling lip of said diaphragm adapted to operate said photoelectric switch. 
     
     
       7. A brake pressure control system as claimed in claim 2, wherein an approach sensor is arranged in the housing which comprises said switch and which provides an electric signal upon approach of said diaphragm. 
     
     
       8. A brake pressure control system as claimed in claim 7, wherein said approach sensor comprises a capacitive sensor arranged in said booster housing, wherein a metal plate is attached to said diaphragm, and wherein said capacitive sensor provides an electric signal upon approach of said metal plate. 
     
     
       9. A brake pressure control system as claimed in claim 7, wherein said booster further includes a metal plate attached to said diaphragm and wherein said approach sensor includes an alternating electromagnetic field disturbed by the approach of said metal plate. 
     
     
       10. A brake pressure control system as claimed in claim 7, wherein said diaphragm has a plate attached thereto, wherein said approach sensor includes a condenser having an electric field, the capacitance thereof disturbed by the approach of said diaphragm plate. 
     
     
       11. A braking pressure control system as claimed in claim 1 wherein said switch means includes a Bowden cable having a core attached to said diaphragm. 
     
     
       12. A braking pressure control system as claimed in claim 11, wherein said switching means includes a travel-responsive switch and a cam member movable by said Bowden cable core and further including a switching ramp on said cam member which actuates said travel-responsive switch after a predetermined movement of said cam member. 
     
     
       13. A brake pressure control system as claimed in claim 1, wherein said switch means comprises a mechanical travel-responsive switch having an element in engagement with said diaphragm to be shiftable therewith so that said switch is actuatable by said diaphragm.